1. Field of the Invention
The present invention relates to asphalt roofing materials with additives that are believed to, among other things, enhance adhesion and/or tear strength of an asphalt coating material used to make the roofing materials, and more particularly wherein the additives include polyphosphoric acid.
2. Description of the Related Technology
As is well known, asphalt is commonly used to make roofing shingles. Typically, the asphalt is used to coat fiberglass mats and then the coated mats are covered with mineral or ceramic granules. This type of shingle is commonly referred to as “fiberglass shingles” and “asphalt shingles.” Although not as prevalent, asphalt is also used to manufacture “organic shingles” in which a cellulose base is saturated in asphalt. Because of the saturation, organic shingles tend to be heavier than fiberglass shingles. Also, organic shingles tend to be less resistant to heat and humidity, but more durable in freezing conditions than fiberglass shingles.
With respect to fiberglass shingles, tear strength is an extremely important characteristic because of the development of fiberglass shingles over the years. Briefly, when fiberglass shingles were first manufactured the fiberglass mat weighed approximately 3.0 lbs/480 ft2 and at that weight with asphalts at the time a minimum tear strength standard of 1,700 grams cross direction (“CD”) was established by the industry. “Cross direction” means performing the tear test at an angle perpendicular to the direction the shingle flowed from the machine (i.e., the “machine direction” or “MD”). Over time, manufacturers, by focusing their research efforts on glass mat technology, have been able to reduce the weight of glass mats, which decreases their material costs. Specifically, the glass mats used widely today are within the range of about 1.5 to about 2.0 lbs/480 ft2. While many fiberglass shingles using lighter weight mats can still satisfy the 1,700 gram tear strength standard, it has prevented the use of even lighter weight mats to produce otherwise acceptable asphalt shingles at still lower costs.
The 1,700 gram standard is a contentious issue between roofing product manufacturers and roofing product purchasers. With purchasers relying almost entirely on tear strength to determine whether fiberglass shingles are defective. The importance of tear strength is illustrated by the fact that litigations between producers and purchasers over the performance of shingles were based primarily on whether shingles satisfied this single property.
Although the manufacturers' efforts to improve the fiberglass mat technology have allowed some reduction in their material costs, those reductions have sometimes been at the expense of acceptable tear strengths. Thus, a need continues to exist for a technology, method, materials, or a combination thereof that would allow roofing manufacturers to reliably produce products with acceptable tear strengths while reducing their costs by, for example, using even lighter weight fiberglass mats.